Internal combustion engines generally installed in vehicles such as straddle type vehicles or the like develop their power output at high speeds of rotation. It is therefore necessary to reduce the speed between the crankshaft and the shaft which drives the wheels. In addition, the torque that the engine delivers can be varied only within narrow limits. For this reason it is necessary to be able to alter the transmission ratio, so that the driving forces applied to the wheels of the straddle type vehicle can be adapted to varying road resistance conditions.
The speed reduction can be obtained by means of a transmission (change-speed gearbox) interposed between a clutch and a final drive. Such a transmission alters the torque that is transmitted. The transmission may include a main shaft, a secondary shaft and an output shaft (connected to the wheels). A multiple disk transmission clutch may be mounted on one end of the main shaft and a dog clutch body, or shift fork, may be slidably mounted on a shaft for changing the transmission gear ratio.
When an operator wants to start the straddle type vehicle with a manual transmission, he has to increase the speed of the engine, gradually depress a clutch lever and move a toe shift pedal in order to engaged the first gear train of the transmission. Having the first speed gear train engaged and increasing the speed, the operator has to depress the clutch lever for disengaging the transmission clutch and move the toe shift pedal in order to change the transmission gear ratio of the engine. Because operation of the clutch lever or toe shift pedal may be disagreeable or difficult, some prior transmission systems have been developed wherein the clutch lever is not present or wherein operation of the toe shift pedal is eased.
U.S. Pat. No. 3,894,442 discloses a semi-automatic gear shifting apparatus for shifting gears in a gear box of a motorcycle. The gears are shifted by rotating a spindle. The spindle is operably connected to a ratchet-type gear shifting means. A lever arm is connected at one end to the spindle and is connected at its other end to a toe pedal of a motorcycle shifting lever arm. A solenoid is mounted on the engine of the motorcycle by means of a mounting bracket. A solenoid connecting rod is operably connected to a core of the solenoid. The rod is operably connected at one end to the toe pedal. The rod is thus reciprocated to move the lever arm and the spindle by the solenoid which is actuated by a pair of push button switches connected to an electrical power source. The spindle is rotated through a relatively small arc. The degrees of the arc are determined by the distance the ratchet is required to move to effect a change in the gears on the gear box.
The semi-automatic gear shifting apparatus is activated when energized selectively through the switches. Each time the apparatus is activated one gear shifting cycle is completed. When the apparatus is de-activated, the lever arm is returned to the neutral position. The use of a gear disengaging clutch (and a clutch lever) is not required here because the movement of the shifting lever arm is sufficiently rapid so as to not damage the gears while effecting the gear shift.
However, experience has shown that under certain operating conditions, the movement of the shifting lever arm may be difficult and a very powerful solenoid is thus required. Moreover, having an exposed solenoid mounted on the engine may be hazardous because its operation may be jeopardized by roadway debris or impediments during driving.
U.S. Pat. No. 5,299,652 discloses a handlebar control system for a motorcycle which enables control of a motorcycle without moving the hands from the handlebars. A shift switch with an up-shift button and a downshift button is provided on a right handlebar while the left handlebar has a normal clutch lever mounted thereon. An advanced shift arm is connected at one end to a shift rod while the other end is connected to an actuator whereby, in operation, the actuator causes movement of the shift arm in order to change the transmission gear ratio. The system also comprises an air compressor which maintains an operating pressure of about 100 p.s.i., a tank, a pneumatic line, an up-shift control solenoid, a downshift control solenoid and an electric circuit connected to a twelve volt battery.
In operation an operator depresses the clutch lever and then the up-shift button which causes the up-shift control solenoid to open to permit a burst of air to flow to the actuator in order to change the transmission gear ratio. Downshifting occurs by pushing the downshift button. The system may also comprise an optional pneumatic kill switch for operating the transmission without using the clutch lever. However, this system requires a lot of space and is not adapted to be mounted in a restrictive area. Moreover, having an exposed actuator may be hazardous because its operation may be jeopardized by roadway debris during driving.
Finally, prior art semi-automatic transmission installed on the straddle type vehicle has some inconveniences such as it still requires the operation of a shift toe pedal. This operation may be difficult because an important effort is required from the operator when the temperature is below a certain point. Also, for an operator who wears large boots, operation of a shift toe pedal may be complicated.
Thus, there is a need in the industry to provide a user-friendly transmission system which eliminates the shift toe pedal.